Both amateur and professional scientists have been obtaining the spectrum of objects for over a century. In the field of astronomy knowing the spectral makeup of a star will tell a lot about it and the area of space where the star is located. One method is by using a telescope and pointing it at a star and inserting a spectrum separating device between the telescope and the observer which will make the star's spectrum visible. In the area of chemistry and physics by knowing the spectral characteristics of an object will help to identify its makeup and other physical parameters of the object.
Currently there are two methods in general use that will separate a beam of light into a spectrum. They are prismatic devices and grating devices. Prismatic devices are generally associated with prisms, which are solid objects made from some sort of transparent material. Grating devices fall into two groups: transmission and reflective. They both share the common ability to separate light into its colors by use of a thin multi-lined grating extending very slightly from one of their surfaces. A common type of material in general use is transparent diffraction grating material.
Grating materials are generally only available as a single plane grating. A single plane grating produces all orders of an object's spectrum in a single horizontal line running symmetrically on both sides of the object's image. This is the commonest type of grating and has been around for many years.
Recently advances in grating technology has produced dual plane gratings. A dual plane grating produces all orders of an object's spectrum in two orthogonal lines, one horizontal and one vertical. It additionally produces two secondary spectrum lines, that are products of the interaction of the two crossed gratings, that produce spectrums that are rotated 45 degrees from the first two orthogonal spectral lines.
In order for the information contained in the spectrum to be of use it generally needs to be recorded or stored. This is usually done by either writing down what information an observer is able to see by looking at the spectrum, or by taking a picture of the spectrum.
Finding a device that will present a lot of the information contained within a spectrum of an object and one that will work with readily available equipment is difficult. The solution would be to use an available camera equipped with a device which would mate to the camera coupled to an appropriate light collector to capture the spectrum.
The current state of art has produced a range of spectrum catching devices like, cameras, storage mediums, and optical capture devices like telescopes both large and small. However, few of these devices will work with the other products needed to produce, store and retrieve a spectrum's information. Different manufacturers gravitate to different solutions depending on their commercial clients. This leaves most of the available spectrum equipment out of the reach of ordinary people's budgets.
Because of the lack of availability for the various equipments required to produce spectrums by the manufacturers of spectrum devices the majority of the users of this type of equipment have gravitated into two widely divergent groups. The first are the commercial users, which also include the larger engineering schools and universities, and the second group is all of the rest. The quality of the spectrum devices available to the last group is severely lacking in spectral detail, available tool sets, compatibility and instruction to use the various components of the system required to capture an object's spectrum.
A typical system, for an individual that desires detailed spectral line information, is to buy one of the SBIG CCD cameras at a cost of several thousand dollars then for an additional cost of several thousands of dollars add a spectrum device that will work only with that camera, but these two items alone aren't sufficient to detail a spectrum so the list goes on and the price tag approaches the tens of thousands of dollars and all just to produce the picture of a small colored line from a bright object. The cost continues to go up as the object becomes dimmer.
This cost is prohibitive for most prospective users and few schools and colleges can spend this level of money for equipment that has such a narrow field of use. If the cost could be reduced significantly without requiring additional equipment costing thousands of dollars more then this exciting field would get more interest and use.
What is needed is a means where the ordinary person can purchase a spectrum device and fix it to their camera and produce a spectrum of an object to include the spectral line information contained within the spectrum.
The most notable use would be for amateur astronomers to be able to use their telescopes equipped with an inexpensive type camera and a spectrum separation device to photograph the spectrum of stars and planets. Another use would be for school teachers to use available CCD cameras to produce spectrum pictures for their students, another use would be for chemical and physical field teams to be able to use small portable, or even throw away, camera systems along with high resolution spectrum recording equipment.
A visual spectrum filter product is made by Rainbow Optics. Here, they insert a single plane grating material inside an eyepiece filter cell to be mounted at the bottom of an eyepiece that is already threaded for standard 1.25″ filters. They have very recently started advertising their visual spectrum device for CCD photography. When it is used with a camera it is mounted external to the camera's lens housing filter threads. The device they sell for CCD use is identical to the unit they sell for visual use. Their device is sold with a cylindrical lens that is used to make the spectrum visually taller but this attachment won't work when attached to a camera as this attachment is strictly for visual use. They are marketing their device for $250. Their device was first produced and sold in 1994 and they have not applied for a patent for it, as far as the inventor has been able to find out. Their web site address is: starspectroscope.com
A second manufacturer makes a model SGS spectrum device for two their own CCD cameras to be used with standard 1.25″ eyepieces. Their unit will not work with cameras made by other manufacturers or with most of their other cameras. Their unit is a large complicated box utilizing a single plane diffraction grating, and LED and other optics to produce the spectrum. Their device is incapable of producing a referenced spectrum. This company is SBIG Astronomical Instruments. Their device without a camera or other hardware sells for $5000.00. They have been marketing this device since 1998 and have not applied for a patent for it, as far as the inventor has been able to find out. Their web site address is: sbig.com
A third manufacturer Baader Planetarium located in Germany also sells a single plane grating unit almost identical to the one made by Rainbow Optics. It is sold strictly as a device to be used for visual observations mounted to an eyepiece and nothing more. Their device is sold with a cylindrical lens that is used to make the spectrum visually taller. As far as the inventor knows they are not advertising their unit for CCD use. As far as the inventor has been able to find out they have not applied for any type of patent on their device. It is not known how long they have been offering their unit. Their web site address is: http://www.baader-planetarium.com/
The devices sold by Rainbow Optics and Baader Planetarium use a 200 l/mm blazed grating that produces a dim low quality spectrum as its spread out very little and has a very narrow bandwidth. This is because it is mounted too far from the sensor. The spectrum their units produce can't be used with dim stars as their spectrum is so tall with their cylindrical lens that its intensity quickly falls below the threshold of light sensors and other capture devices. Using a cylindrical lens with these devices will also distort the image of the spectrum as well as greatly reduce its intensity. As such these devices are generally limited to 3rd or 4th magnitude stars because of their visual design, while the magnitude limit of the present invention exceeds 11th magnitude stars.
A major problem with using these two devices on a CCD camera is that because they use a 200 lines/mm grating the spectral image is exceedingly small on the CCD chip, usually covering less than 20% of the chips width. Such small use of the chip results in extremely low resolution spectrums with little to no contained information content.
Another major drawback with their product is that they both use a blazed grating. Their gratings are designed for visual use with a blaze wavelength of 550 nm. This greatly reduces the bandwidth of their devices which is generally limited to 420 nm to 670 nm. The bandwidth of most inexpensive CCD cameras extends from 390 nm to over 950 nm so using a blazed grating with these cameras greatly reduces the bandwidth gain these cameras are capable of producing.
Another drawback with using blazed gratings is the spectrums they produce are bell shaped, with respect to intensity versus wavelength efficiency, instead of producing flat spectrums as is generated by non-blazed gratings. This makes calibration of the spectrum blazed gratings produce very difficult.
One of the many objections users have with devices from these two companies is that their devices are designed strictly for visual use and as such it is extremely difficult to adapt them to work on a CCD camera. Their units were only designed to be used with a threaded telescope eyepiece and they don't offer any adapters to fit most CCD cameras, and neither of these two companies offer any device that is designed to fit inside the lens housing of a camera or offer a devise designed to fill the film plane or CCD chip of a camera. Because of the course grating that they both use in their devices the spectrums produced are of little value due to the low resolution available with course gratings, and it is extremely difficult to resolve and identify individual spectral lines with their devices which is the main purpose of capturing an object's spectrum.
The device sold by SBIG is priced far too high to bring it into general use. While this device does produce photographable spectrums of good resolution it doesn't perform well with dim stars due to the extra light loss within their system. While their device does produce a high quality spectrum, it does not produce a reference spectrum and requires a very complicated means to determine the spectrum's wavelength information. They do not offer Angstrom level referencing or calibration tools with their unit and leave this complicated task to the user to solve on their own. Their device will only work with two of the many cameras that they made and will work with no other cameras made by anyone else.
It is therefore an object of the invention to produce a reference spectrum.
It is another object of the invention to produce a compact spectrum.
It is another object of the invention to produce a high resolution spectrum.
It is another object of the invention to produce a spectrum of an object.